Nickel-based catalyst, its preparation and its application

ABSTRACT

A hydrogenation catalyst is disclosed, said catalyst consisting essentially of 10-90 parts by weight of nickel and 90-10 parts by weight of silica and having an overall active nickel surface area of 70-200 m 2  /g. A two-step process for preparing the catalyst is also disclosed.

The invention relates to a nickel-based catalyst, to its preparation andto its application for hydrogenation reactions.

Nickel-based catalysts are well-known and are widely used ashydrogenation catalysts. It is customary to prepare them byprecipitating nickel-hydroxide and/or -carbonate from an aqueoussolution of a nickel salt using an alkaline reactant, often in thepresence of a carrier.

In the preparation of these catalysts measures are often taken toprecipitate the insoluble nickel compounds as gradually as possible fromthe solution onto the carrier particles suspended therein. To this end,for example, a carrier suspension in a solution of a nickel-ammoniacomplex is heated so as to allow the ammonia to escape, thereby causingthe nickel to precipitate (cf. GB-A-No. 926 235). Alternatively, urea isincorporated in the solution in which the carrier is suspended, afterwhich the urea is decomposed by heating (cf. GB-A-No. 1 220 105),causing the nickel hydroxide to precipitate. The aim of this verygradual precipitation of the nickel is to cover the carrier particlesentirely or largely with nickel compound. Furthermore, GB-A-No. 1 367088 discloses the preparation of a catalyst by precipitating nickel onguhr, keeping temperature, pH, alkalinity and residence time withinnarrow ranges. In this process the nickel hydroxide is slowlyprecipitated from a diluted solution in a reaction vessel, after whichthe solid components are separated. Precipitation and post-reaction (thelatter normally being referred to as "ageing") take place in the samereaction vessel, which therefore has to be relatively big, under thesame reaction conditions.

It has now been found however that new, improved nickel-based catalystscan be prepared by carrying out this process in at least two separatesteps, to wit: (i) A very rapid precipitation step, in which undervigorous agitation the nickel hydroxide/carbonate is precipitated in aprecipitation reactor with a mean residence time of 0.01 to 10,preferably 0.2 to 4.5 minutes, rather even less than 3.5 minutes, duringwhich the nomality of the solution in the reactor, containing excessalkali, is between 0.05 an 0.5, prefereably between 0.1 and 0.3N and thetemperature of the liquid in the precipitation reactor is kept between5° and 95°, preferably between 20° and 55° C. (ii) At least oneseparate, longer ageing step with a mean residence time in thepost-reactor of 20 to 180 min, and a temperature that remains between60° and 100°, preferably between 90° and 98° C. It is sometimespreferred for the temperature during the ageing step(s) to differ fromthat during the precipitation step; in particular it may be advantageousto perform the ageing step at somewhat higher temperatures, e.g. with adifference of 10° C. above the precipitation temperature.

The nickel-based catalysts according to the present invention comprise awater-insoluble carrier material which is present or added duringpreparation. Suitable carrier materials are, for example,silica-containing materials such as kieselguhr, aluminium trioxide, andsilicates such as bentonite. Kieselguhr is the preferred material,particularly kieselguhr containing from 50 to 90 wt. % of amorphoussilica.

The carrier material can be added (a) directly as such, (b) as anaqueous suspension, (c) preferably as a suspension in an aqueous nickelsalt solution, (d) as a suspension in an aqueous solution of thealkaline compound.

According to embodiments (a)-(d) the carrier can be added before orduring precipitation. According to embodiments (a), (b) or (d), however,the carrier can also be added entirely or partly (the latter beingpreferred) after precipitation, but also before or during ageing.

After precipitation and ageing according to the invention the solids areseparated from the liquid, optionally washed, dried and activated bycontacting them with hydrogen at an elevated temperature in a mannerknown per se.

Nickel compounds which can be used as starting materials for thepreparation of the catalysts according to the present invention arewater-soluble nickel compounds such as nitrate, sulphate, acetate andchloride. The solutions that are fed into the precipitation reactorpreferably contain between 10 and 80 g nickel per liter; particularlypreferred is the use of solutions containing between 25 and 60 g nickelper liter.

Alkaline compounds which can be used as starting material in the processaccording to the present invention are alkalimetal hydroxides,alkalimetal carbonate, alkalimetal bicarbonate, the correspondingammonium compounds and mixtures of the above-mentioned compounds. Theconcentration of the alkaline solution fed into the precipitationreactor is preferably 20-300 g of anhydrous material per liter (as faras the solubility permits this), particularly between 50 and 250 g perliter.

It has practical advantages to use the two solutions (nickel-containingand alkaline, respectively) in about equal concentrations expressed inequivalents, resulting in the use of about equal volumes.

The nickel-containing solution and the alkaline solution are fed at suchrates that a slight excess of alkaline compound is present during theprecipitation step, namely such that the normality of the liquid rangesfrom 0.05 to 0.5, preferably from 0.1 to 0.3 (said normality beingdetermined by titration with aqueous hydrochloric acid usingmethylorange as the indicator). In the ageing step it may sometimes bedesirable to add further alkaline solution in order to maintain thealkalinity (normality) in the above-defined range.

The precipitation reactor comprises a means for vigorous agitation ofthe reacting fluid and its dimensions are such in relation to theamounts of fluid fed that the short mean residence times indicated canbe obtained. Preferred mean residence times in the precipitation reactorare normally between 0.01 and 10, particularly between 0.2 and 4.5minutes. The precipitation step and also the ageing step can be carriedout batchwise, continuously and semi-continuously (e.g. according to thecascade method).

In the preferred continuous precipitation process (step i) the rate ofaddition of the solutions to the precipitation reactor is controlled bycontinuously or discontinuously measuring the alkalinity (normality) ofthe discharged liquid. This can sometimes also be done by monitoring thepH. Also the temperatures of the reacting liquids fed into theprecipitation reactor are used to control the temperature at whichprecipitation takes place. The required vigorous agitation of the liquidin the precipitation reactor preferably takes place with an energy inputof 5-25 K watts per 1000 kg of solution. Jet mixing is also a suitablemethod, involving much larger specific energy inputs of up to 2000 Kwatts/kg.

The reaction mixture obtained from the precipitation reactor issubsequently led into a significantly larger post-reactor, in which theliquid is further agitated. If desired, additional ingredients can beincorporated here, such as carrier material, alkaline solution asdefined hereinbefore and/or possibly promoters.

Preferably the temperature of the liquid in the post-reactor, i.e.during the ageing step, is kept at a temperature between 60° and 100°C., preferably between 90° and 98° C.

The normality of the liquid in the post-reactor during the ageing step(step ii) is kept in the same range as during the precipitation step(step i); it may be required to add some further alkali. The ageing stepcan be performed in one or more post-reactors, the (overall) meanresidence time bing kept between 20 and 180 min, preferably between 60and 150 min. If two or more post-reactors are used it is desirable toarrange this in such a way that in the second or following post-reactorthe temperature of the liquid is 10 to 15 centrigrades below thetemperature in the first post-reactor.

After completion of the ageing step the solids are separated from themother liquor, usually washed, dried, optionally ground and/orcalcinated and subsequently activated with hydrogen gas at an elevatedtemperature usually ranging between 250° and 500°, preferably between300° and 400° C. This activation can take place at atmospheric or higherpressure. Atmospheric pressure is preferred.

Preferably before drying, or during any previous step promoters canconveniently be added. Promoters comprise amounts of 0.05 to 10%,calculated on the weight of nickel, of metals/compounds such as copper,cobalt, zirconium, molybdenum, silver, magnesium, any other metals andcombinations thereof.

The separated solid is preferably washed with water, sometimes madeslightly alkaline, or water with a detergent added thereto.

Organic solvents can sometimes be used advantageously. Drying takesplace preferably with forced air circulation. Spray-drying andfreeze-drying are also quite well possible.

The present invention provides new, improved nickel-based catalystswhich comprise 10-90 parts by weight of nickel/nickel compounds and90-10 parts by weight of insoluble carrier material, as well as 0-10,preferably 0.05-5 parts by weight of a metal promoter, which catalystshave an active nickel surface of 70-200 m² /g, preferably more than 100m² /g, said catalysts further comprising aggregates which mainly consistof nickel/nickel compounds with an average particle size of 2 to 100micrometers, preferably between 5 and 25 micrometers, and whichaggregates have an (outer) surface which is for at least 60% free ofcarrier particles attached thereto. Preferably the nickel/nickelcompound aggregates have a surface which is for more than 80%,particularly for more than 90% free of carrier particles.

The nickel/nickel compound aggregates consist mainly, i.e. for more than80%, preferably more than 90%, of nickel and nickel oxides, but somepromoter material may also be present. These aggregates preferablycontain nickel crystallites with an average diameter between 0.5 and 10,more particularly between 1 and 3 nanometers.

The catalyst according to the invention is used for the hydrogenation ofunsaturated organic compounds, in particular oils and fats, fatty acidand derivatives thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are micrographs of the inventive catalyst.

The invention is illustrated by the following Examples.

EXAMPLE 1

An aqueous suspension was prepared by suspending kieselguhr (containing7.0% amorphous SiO₂) in a NiSO₄ solution (35 g Ni/1 and 1.2N), in such away that the Ni:SiO₂ -ratio was 1:2.3. Also an aqueous soda solution,containing 75 g of Na₂ CO₃ (anh) per liter and 1.4N, was prepared.Subsequently both solutions were continuously pumped into a vigorouslyagitated pump reactor, in about equal volumes, resulting inprecipitation of nickel hydroxide/carbonate at a temperature of 80° C.The alkalinity of the suspension so obtained was 0.096N. In the reactorin which the precipitation took place the suspension had a residencetime of 4 minutes, after which the suspension was immediately passed tothe first of a series of two post-reactors. In each of thesepost-reactors the precipitate was aged for 50 minutes (mean residencetime) at temperatures of 97° and 80° C., respectively. The agedprecipitate was then continuously filtered off and the green filter cakethus obtained was washed with water, dried and activated with hydrogenunder atmospheric pressure at a temperature of 350° C.

Electron microscopy and microrontgen analysis showed that the catalystconsisted of nickel crystallites averaging 2 nanometers and aggregatesaveraging 21 micrometers. The surface of the nickel/nickel compoundaggregates was for about 85% free of carrier particles and also theoriginal shape of the silliceous skeletons was largely uncovered andwell and freely perceptible.

EXAMPLES 2-7

Following the procedure as described in Example 1 further catalysts wereprepared according to the invention, while varying the amounts andconditions, as is shown in Table I. Measures were taken to keep theother conditions unchanged.

In Table II, showing the hydrogenation characteristics of this catalyst,comparisons are made with a catalyst known from the literature.

On fatty acid hydrogenation it was found that for achieving a certainiodine value, with catalyst according to the invention less than halfthe hydrogenation time was sufficient and that in the case of fish oilthe catalyst also retained its activity for a longer period. From themelting points it appeared that the new catalyst had a greaterselectivity, i.e. less tri-saturated triglyceride was formed.

On fatty acid hydrogenated it turned out that hydrogenation could becarried through to lower iodine values in the same hydrogenation timeand thus proceeded more rapidly than with the known catalyst used forcomparison. Furthermore, the hydrogenations can also be performed withexcellent results at a lower hydrogenation temperature. In addition, thenew catalyst could be filtered very effectively, in any case better thanthe known catalyst.

Table III below gives an impression of fatty acid hydrogenation plottedagainst time (relation between iodine value and hydrogenation time underotherwise equal conditions).

                  TABLE III                                                       ______________________________________                                        Hydrogenation                                                                              Iodine value                                                                              Iodine value with                                    time         with catalyst 4                                                                           known catalyst                                       (min)        (Table II)  (Table II)                                           ______________________________________                                        30           45.1        72.1                                                 60           15.3        45.5                                                 90           9.8         22.2                                                 120          5.3         17.8                                                 150          3.3         15.1                                                 ______________________________________                                    

Table III demonstrates that the iodine value of the hydrogenated fattyacid of about 15.2, obtained with the conventional catalyst widely usedfor this purpose after about 150 minutes, was already reached in about60 minutes with the catalyst according to the invention, which is aconsiderable technological improvement.

                                      TABLE I                                     __________________________________________________________________________    Example:      1   2   3  4   5   6  7                                         __________________________________________________________________________    Ni:SiO.sub.2 ratio                                                                          2.3 2.3 2.3                                                                              2.3 2.3 1.8                                                                              1.8                                       Precipitation                                                                 Conc. soda solution, mol/l                                                                  0.7 0.7 0.7                                                                              0.7 0.7 0.7                                                                              1.0                                       Conc. nickel solution, mol/l                                                                0.6 0.6 0.6                                                                              0.6 0.6 0.6                                                                              0.6                                       Precipitation temp. (°C.)                                                            80  20  30 55  50  85 22                                        Mean resid. time (step 1), min                                                              4   1   1  1   1   0.3                                                                              0.5                                       Excess alkali (normality)                                                                   0.10                                                                              0.19                                                                              0.21                                                                             0.22                                                                              0.21                                                                              0.13                                                                             0.21                                      Ageing of precipitate                                                         Number of post-reactors                                                                     2   2   1  2   2   1  1                                         Temperature (°C.)                                                                    97/80                                                                             97/80                                                                             96 93/80                                                                             90/77                                                                             95 97                                        Mean resid. time                                                              (step 2) in minutes                                                                         50/50                                                                             50/50                                                                             50 50/50                                                                             85/50                                                                             30 30                                        Excess alkali (mol/l)                                                                       0.135/                                                                            --  -- --  --  -- --                                                      0.192*                                                          __________________________________________________________________________      *extra alkali                                                                Catalysts 1-5 contained 70% nickel and 30% SiO.sub.2 ; catalysts 6 and 7      contained 64% nickel and 36% SiO.sub.2.                                       Active nickel surfaces ranged between 120 and 150 m.sup.2 /g nickel.           Nickel aggregates were found to range between 9 and 26 micrometers and       the catalyst of Example 4 was shown to have nickel aggregates which prove     to be for 85% free of carrier particles.                                 

                                      TABLE II                                    __________________________________________________________________________                                      Compar.                                     Example     1  2  3  4  5  6  7   example                                     __________________________________________________________________________    Ni % in reduced                                                                           52.4                                                                             51.8                                                                             52.6                                                                             53.0                                                                             52.7                                                                             51.2                                                                             52.0                                                                              22                                          catalyst                          (in fat                                     Oil hydrogen. test                susp.)                                      refined marine oil of                                                         I.V. 165 to 85;                                                               conditions:                                                                   250 g oil, 0.1% Ni                                                            on oil, 60LH.sub.2 /h                                                         press. 1 bar, max. temp.                                                      180° C., 750 rpm, reduct.                                              temp. of cat. 350° C.                                                  Hydrogen. time (min)                                                                      92 85 83 92 85 90 103 127                                         m.p. of oil (°C.)                                                                  32 32.5                                                                             32 32.5                                                                             32.5                                                                             33 32.5                                                                              36                                          fatty acid hydrog. test                                                       300 g tallow fatty acid                                                       (olein fraction)                                                              0.07 Ni on fatty acid,                                                        H.sub.2 press. 30 bar max.                                                    temp. 180° C.                                                          Stirring speed 850 rpm                                                                    3.1                                                                              2.5                                                                              3.2                                                                              3.3                                                                              2.6                                                                              3.4                                                                              3.0 15.1                                        hydrog. time 150 min                                                          reduction cat. 350° C.                                                 I.V. after hydr.                                                              __________________________________________________________________________

EXAMPLE 8

A 10% aqueous soda solution and a 3.5% aqueous nickel sulphate(calculated as nickel) solution in which kieselguhr (22 g per liter) hadbeen blended were both continuously pumped into a small precipitationreactor (75 ml capacity) whilst the reactor was heavily agitated (energyinput 6 Watts per liter of solution). The two liquids were fed into thereactor in such rates that the pH in the precipitation reactor was 9.3.The residence time was 0.5 minutes.

After precipitation the slurry contained about 4% of solids and thisslurry was continuously aged in a relatively larger vessel (capacity4.5 1) with moderate stirring. The ageing temperature was 97° C. and thepH was 8.9. The average residence time in the ageing reactor was about30 minutes.

After 1.5 hours the flows were stopped and 4.5 1 of slurry were filteredin a Buchner funnel under vacuum. After filtration the solids (filtercake) were washed with 4 liters of distilled water. The filter cake wasthen dried overnight in an oven at 120° C.

Samples of the green filter cake were investigated by electronmicroscopy (magnification 500 and 1000x). The photos as described inFIGS. 1 and 2 showed small nickel/nickel compound aggregates of which80% were free of carrier particles and also the original shapes of thesiliceous skeletons were largely uncovered by nickel/nickel compoundsand freely perceptible.

The green cakes were reduced at 400° C. with a hydrogen flow of 15 N*m³/kg Ni for 30 minutes.

The active nickel surface area was determined by hydrogen chemisorptionand yielded a value of 110m² /g nickel. The average size of the nickelcrystallites was calculated to be 3 nanometers and the size of thenickel/nickel compound aggregates was found to be 30 micrometers.

This catalyst had excellent properties for the hydrogenation of soybeanand fish oils.

We claim:
 1. Hydrogenation catalyst consisting essentially of 10-90parts by weight of nickel and 90-10 parts by weight of silica and havingan overall active nickel surface of 70-200 m² /g per gram nickel,characterized, in that the catalyst comprises nickel/nickel compoundaggregates which have an average particle size ranging from 2 to 100micrometers and wherein the aggregates have an outer surface which is atleast 60% free of carrier particles.
 2. Hydrogenation catalyst accordingto claim 1, characterized in that the outer surface of the aggregates isat least 80% free of carrier particles.
 3. Hydrogenation catalystaccording to claim 1, characterized in that the aggregates have an outersurface which is at least 90% free of carrier particles. 4.Hydrogenation catalyst according to claim 1, characterized in that theaverage particle size of the nickel/nickel compound aggregates rangesbetween 5 and 25 micrometers.
 5. Hydrogenation catalyst according toclaim 1, characterized in that the aggregates have an average nickelcrystallite size which ranges between 0.5 and 10 nanometers. 6.Hydrogenation catalyst according to claim 5, characterized in that thenickel crystallite size ranges from 1 to 3 nanometers.
 7. Ahydrogenation catalyst according to claim 1 wherein the overall activenickel surface area is 100 to 200 m² /g per gram of nickel.
 8. Processfor preparing a nickel-based catalyst comprising an insoluble carrier,which process comprises:(i) a rapid precipitation step, in which undervigorous agitation nickel hydroxide/carbonate is precipitated by feedinga nickel-containing solution and an alkaline solution into aprecipitation reactor with a mean residence time of 0.01 to 4.5 minutes,during whick the normality of the solution in the reactor, containingexcess alkali, is between 0.05 and 0.5, and the temperature of theliquid in the precipitation reactor is kept between 5° and 95° C., (ii)and thereafter employing at least one separate, longer ageing step witha mean residence time in a post-reactor of 20 to 180 minutes and atemperature that remains between 60° and 100° C., after which the solidis separated, dried and activated with hydrogen and wherein thetemperature of the rapid precipitation step is at least 10° C. lowerthan that of the ageing step.
 9. Process according to claim 8,characterized in that the nickel salt solution to be precipitatedcontains 10-80 g nickel per liter.
 10. Process according to claim 8,characterized in that the carrier is added before or duringprecipitation in an amount of 20-200 g per liter.
 11. Process accordingto claim 1, characterized in that the solution of the alkaline compoundcontains from 30 to 300 g of anhydrous alkaline compound per liter. 12.Process according to claim 8, characterized in that the alkalinesolution contains sodium carbonate.
 13. Process according to claim 8,characterized in that the nickel compound is a salt of a mineral acid.14. Process according to claim 8, characterized in that the carrier issilica.
 15. Process according to claim 14, characterized in that thesilica used in kieselguhr consisting of 50 to 90 wt. % of amorphousSiO₂.
 16. Process according to claim 8, characterized in that duringprecipitation agitation takes place with a mechanical energy input of5-2000, Kilowatts per 1000 liters of solution.
 17. Process according toclaim 8, characterized in that agitation is effected by jet mixing. 18.Process according to claim 8, characterized in that the activation ofthe catalyst is carried out with hydrogen at a temperature between 250°and 500° C.
 19. Process according to claim 8, characterized in thatprecipitation is carried out continuously by dosing a carrier suspensionin an aqueous nickel salt solution together with an alkaline solutionand subsequently pumping the suspension into at least one post-reactors.20. Process according to claim 19, characterized in that at least twopost-reactors are used, the temperature in the second and subsequentpost-reactor being 5°-15° C. lower than that in the first post-reactor.21. A process according to claim 8 wherein the mean residence time instep (i) is 0.2 to 4.5 minutes and in step (ii) is 60 to 150 minutes,the normality of the solution in step (i) is between 0.1 and 0.3 N, thetemperature of the liquid in the reactor in step (i) is between 20° and55° C. and the temperature in step (ii) is between 90° and 98° C. 22.Process according to claim 16 wherein the mechanical energy input is5-25 kilowatts per 1000 liters of solution.